Pneumonia remains the leading infectious cause of morbidity and mortality in the United States. In spite of its substantial public health burden, recent measurements of pneumonia incidence in the United States are surprisingly scarce and differences in research methodologies make the comparison of available estimates problematic. Moreover, our current knowledge of the distribution of etiologic organisms for community-acquired pneumonia (CAP) is limited and largely based on case series or studies performed decades ago or abroad. The availability of novel molecular techniques provides opportunities to reassess this knowledge systematically. Without current large-scale population-based studies to inform clinicians about the most likely etiologies of pneumonia and the identification of resistant organisms, clinicians would continue to assess and treat patients with pneumonia as they have for the past several decades. Since January 2010 we have conducted active population-based surveillance for pneumonia in subjects of all ages through the CDC-funded study, The incidence and etiology of influenza-associated pneumonia in hospitalized persons. The procedures for enrolling and testing eligible pneumonia patients have been well established; data collection forms have been developed and tested; CDC-endorsed laboratory procedures have been established; extensive data are now being collected and systematically entered into the master project databases; and radiographs from each pneumonia case are being evaluated by study radiologists. With these well established study methodologies and experience, we are well positioned to continue the CDC-funded pneumonia project for two additional years. We propose to use our existing infrastructure, skilled personnel, network capabilities, and previous experience to perform a multicenter, population-based, prospective cohort study to determine the incidence and etiologies of pneumonia leading to hospitalization for both children and adults. Our project encompasses the following specific aims: 1)To determine the incidence of hospitalization for community- acquired pneumonia in children and adults living in Middle Tennessee; 2) To determine the relative contributions of the different respiratory pathogens to the etiology of community-acquired pneumonia in children and adults hospitalized in Middle Tennessee; and, 3)To establish the burden of influenza associated with community-acquired pneumonia in children and adults hospitalized in Middle Tennessee.